In the ideal world, a system will be created to cater for every eventuality and have no mistakes or unconsidered events. In the real world, mistakes and unexpected events happen.
Many computer software development systems offer assistance to a developer as software is being written. One way is via dynamic analysis.
Dynamic analysis (or dynamic testing) is a term used in software engineering to describe the testing of the dynamic behaviour of code. That is, dynamic analysis refers to the examination of the physical response from the system to variables that are not constant and change with time. In dynamic analysis, the software must be compiled and run. An error (either an exception or a spurious result) that arises at this stage is referred to as a run-time error. An exception, if handled properly in code may not even be seen by a user and may simply be logged or stepped over. Nevertheless, it is still desirable to eliminate such exceptions to avoid reduced functionality (the exception presumably occurred while the system was supposed to be doing something useful) or unintended consequences. Dynamic analysis tends to focus at relatively low levels of program functionality, dealing with variable settings and the like.
Unit Tests, Integration Tests, System Tests and Acceptance Tests are a few of the existing dynamic testing methodologies. Dynamic testing typically means testing based on specific test cases by execution of the test object or running programs.
Just because a computer program passes dynamic testing does not necessarily mean it is free from issues. One area that is difficult to test with dynamic testing is functional behaviour such as: how an interface reacts to user inputs; or what happens when the program is in a particular state (such as user logged on or not logged on) and a specific action is performed. Actions may be non-user specific and concerned with the environment and/or inputs from external systems.